Re: [PATCH v1 1/3] KVM: arm64: Initialize HCRX_EL2 traps in pKVM

[Marc Zyngier <maz@kernel.org>]

On Wed, 26 Feb 2025 10:07:56 +0000,
Oliver Upton <oliver.upton@linux.dev> wrote:
> 
> Hi Fuad,
> 
> Series LGTM overall, one comment:
> 
> On Fri, Feb 14, 2025 at 03:02:56PM +0000, Fuad Tabba wrote:
> > Initialize and set the traps controlled by the HCRX_EL2 in pKVM
> > when the register is supported by the system.
> > 
> > Signed-off-by: Fuad Tabba <tabba@google.com>
> > ---
> >  arch/arm64/kvm/hyp/nvhe/pkvm.c | 46 ++++++++++++++++++++++++++++++++++
> >  1 file changed, 46 insertions(+)
> > 
> > diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
> > index 3927fe52a3dd..668ebec27f1b 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
> > @@ -58,6 +58,30 @@ static void pkvm_vcpu_reset_hcr(struct kvm_vcpu *vcpu)
> >  		vcpu->arch.hcr_el2 |= HCR_ATA;
> >  }
> >  
> > +static void pkvm_vcpu_reset_hcrx(struct pkvm_hyp_vcpu *hyp_vcpu)
> > +{
> > +	struct kvm_vcpu *host_vcpu = hyp_vcpu->host_vcpu;
> > +	struct kvm_vcpu *vcpu = &hyp_vcpu->vcpu;
> > +
> > +	if (!cpus_have_final_cap(ARM64_HAS_HCX))
> > +		return;
> > +
> > +	/*
> > +	 * In general, all HCRX_EL2 bits are gated by a feature.
> > +	 * The only reason we can set SMPME without checking any
> > +	 * feature is that its effects are not directly observable
> > +	 * from the guest.
> > +	 */
> > +	vcpu->arch.hcrx_el2 = HCRX_EL2_SMPME;
> > +
> 
> The comment isn't wrong, but we don't support SME at all in KVM at this
> point.

This is a copy/paste of what we have in kvm_calculate_traps(), and the
result of the removal of the dreaded HCRX_GUEST_FLAGS.

> Any objection to dropping this bit? I can fix it when applying the
> series, no need to respin.

Whatever we do, I think we should keep the two side of the trap
configuration in sync, as this is otherwise a cause of bugs.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.